Visual Basic

Business Objects

Business objects are big news. Everyone says the key to building distributed enterprise applications is business objects. Lots of 'em. Business objects are cool and funky-we need business objects! You need business objects! Everyone needs business objects!

This chapter presents a design pattern for developing solid, scalable, robust business objects, designed for (and from) real-life distributed enterprise applications.

The architecture we propose at The Mandelbrot Set (International) Limited (TMS) for building distributed business object-based applications breaks down into various layers of functionality.

The data access layer (DAL) is the layer that talks to the data source. The interface of this layer should be the same regardless of the type of data source being accessed.

The business object layer is the actual layer that models the entities within your application-the real data, such as Employees, Projects, Departments, and so forth. In Unified Modeling Language (UML) parlance, these are called entity objects.

The action object layer represents the processes that occur on the business objects: these processes are determined by the application requirements. In UML, these action object layers are called control objects.

The client application layer, such as a Microsoft Visual Basic form, an ActiveX document, or an Active Server Page (ASP) on a Web server, is known as an interface object in UML.

This chapter concentrates on the middle business object layer and introduces the concepts of action objects, factory objects, and worker objects.